The present invention relates to chokes and starting aids for small internal combustion engines and, more particularly, to a choke and starting aid which enhances cold starting, cold run and flooded starting conditions.
When starting small internal combustion engines, it is usually necessary to pull on the starter rope several times before the engine kicks over and begins to run. Generally, after a couple of pulls on the starter rope, the engine starts and runs for a short period of time and then stops. This "false start" phenomenon has been present in the chain saw art for several years and has come to be accepted by users of such saws as an acceptable starting method. The user generally has knowledge of the fuel system procedure and understands why the system is not starting.
The difficulty in starting a cold small internal combustion engine centers around the choke system of these particular engines. When the choke system is in a closed position, the fuel line system of a cold engine has a very high restriction in the air intake. This restriction of the air intake forms a vacuum in the fuel line, sucking fuel into the engine, via the carburetor, from the fuel tank. Also, a fuel bulb or the like may be coupled with the engine to force the fuel into the carburetor. Two such fuel bulb systems are illustrated in U.S. Pat. Nos. 4,793,951 (issued Dec. 27, 1988) and 4,684,485 (issued Aug. 4, 1987), both assigned to the assignee of the present application, the specifications of which are expressly incorporated by reference.
As the starting rope is pulled, the engine sucks fuel into the carburetor by the vacuum created in the system. As the engine begins to fire, a certain amount of air is necessary to keep the engine running. With a manual choke, the user must open the choke quickly after the engine begins to run or the user will experience the "false start" phenomenon. The reason for the "false start" is that as the speed of the engine increases, the engine sucks more fuel. With the choke in a closed position, however, the amount of air flow entering the engine is not increased. Thus, a proper mixture of air and fuel is not achieved and the engine dies instantly. Also, if the engine does not start, a substantial amount of fuel is sucked into the engine, via the carburetor, causing the engine and carburetor to become flooded, further hampering the starting procedure of the engine.
Choke devices presently used in the field are of a butterfly type. These types of chokes are pivotally secured in the carburetor air port of an internal combustion engine. The choke usually pivots about a central axis, rotating from a closed to an open position. This type of choke assembly has several disadvantages. When starting the engine the choke is in the fully closed position. Once the engine starts, it is nearly impossible to rotate the choke to its open position, so that the engine will continue to run. Also, the butterfly valve may move from a closed to an open position without notice to the user. This slippage is due to the fact that, in many instances, there is no resistance member holding the butterfly valve in position. Those skilled in the art are aware of yet other disadvantages of this type of choke assembly.
Another type of choke device that is present in the art is disclosed in U.S. Pat. No. 4,711,744 issued Dec. 8, 1987 to the assignee of the present invention, the specification of which is expressly incorporated by reference. This type of device works well in monitoring the amount of air entering into the internal combustion engine.
Another type of automatic choke device that is present in the art is disclosed in U.S. Pat. No. 4,948,536, issued Aug. 14, 1990, to the assignee of the present application, the specification of which is expressly incorporated by reference. This device works well to provide sufficient combustion air during start-up and continuous run conditions, however, designers are always striving to improve the art.
Accordingly, it is an object of the present invention to overcome the disadvantages of the above art. The present invention provides the art with a new and improved choke assembly which enables air to automatically enter the carburetor during start-up of an internal combustion engine to provide a continuous running situation. The present invention includes a mechanism responsive to pressure differentials in the internal combustion engine which, in turn, controls the amount of air entering into the engine. The present invention provides the automatic choke to be in a choked condition with the throttle in a partially open condition at cold start-ups. Also, the present invention provides the automatic choke to be in an open position with the throttle in a wide open condition to enhance starting in a flooded or hot restart condition. The present invention provides a one piece starting aid which partially restricts the air flow during cold start-ups.
From the subsequent description and the appended claims taken in conjunction with the accompanying drawings, other objects and advantages of the present invention will become apparent to those skilled in the art.